Swift 6 suitable notification observers in iOS

I have a couple of side projects going on, although it is always a challenge to find time of them. One of them, SignalPath, is what I created back in 2015. Currently, I have been spending some time to bump the Swift version to 6 which brought a quite a list of errors. In many places I had code what dealt with observing multiple notifications, but of course Swift 6 was not happy about it.

	let handler: (Notification) -> Void = { [weak self] notification in
	self?.keyboardInfo = Info(notification: notification)
	}
	let names: [Notification.Name] = [
	UIResponder.keyboardWillShowNotification,
	UIResponder.keyboardWillHideNotification,
	UIResponder.keyboardWillChangeFrameNotification
	]
	observers = names.map({ name -> NSObjectProtocol in
	return NotificationCenter.default.addObserver(forName: name,
	object: nil,
	queue: .main,
	using: handler)
	// Converting non-sendable function value to '@Sendable (Notification) -> Void' may introduce data races
	})

view raw Observer.swift hosted with ❤ by GitHub

After moving all of the notification observing to publishers instead, I can ignore the whole sendable closure problem all together.

	Publishers.Merge3(
	NotificationCenter.default.publisher(for: UIResponder.keyboardWillShowNotification),
	NotificationCenter.default.publisher(for: UIResponder.keyboardWillHideNotification),
	NotificationCenter.default.publisher(for: UIResponder.keyboardWillChangeFrameNotification)
	)
	.map(Info.init)
	.assignWeakly(to: \.keyboardInfo, on: self)
	.store(in: &notificationCancellables)

view raw Observer.swift hosted with ❤ by GitHub

Great, compiler is happy again although this code could cause trouble if any of the notifications are posted from a background thread. But since this is not a case here, I went for skipping .receive(on: DispatchQueue.main). Assign weakly is a custom operator and the implementation looks like this:

	public extension Publisher where Self.Failure == Never {
	func assignWeakly<Root>(to keyPath: ReferenceWritableKeyPath<Root, Self.Output>, on object: Root) -> AnyCancellable where Root: AnyObject {
	return sink { [weak object] value in
	object?[keyPath: keyPath] = value
	}
	}
	}